Dynamics Simulation Model Research Articles

(Keynote) Spectroscopic and Theoretical Studies of HOR/HER Electrochemical Interfaces

Hydrogen fuel cells and water splitting electrolyzers are clean electrochemical devices toward the sustainable utilization of H2 as an energy carrier to replace traditional fossil fuels, in which hydrogen oxidation and evolution (HOR/HER) are two key reactions. Regardless of the apparent simplicity of these two reactions that involve *H as the only surface intermediates, the reaction mechanisms are still under intensive debate.It has been well reported that the HOR/HER kinetics in alkaline media is about two orders of magnitude slower than that in acid environment on Pt-group metals, while the reasons are not fully revealed. In this work, power surface-enhanced infrared absorption spectroscopy (SEIRAS) is utilized to directly monitoring the structures of HOR/HER electrochemical interfaces in a wide pH range. Through the changes of vibrational wavenumbers of Pt-H and O-H stretching, we find both the weakened *H and H2O binding strength on Pt as the solution pH increases, which are important contributions to the lowered reaction kinetics. Through constructing density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulation models that contain various interfacial parameters, HER activation energy barriers as a function of pH are further elaborated.In addition, Ru adatoms have been found to significantly accelerate HER/HOR kinetics on Pt in alkaline media. However, the promotion mechanism is unclear. Through directly monitoring the vibrational features of Pt-H and Ru-H on Ru-modified Pt thin films, we find that the HER/HOR kinetics is proportional to the Ru coverage, which unambiguously demonstrates Ru overlayer as the true active sites, instead of an auxiliary to Pt through the oxophilicity or alloying effects as proposed previously. DFT calculations illustrate that the strain and electronic effects of the Pt substrate lead to the more suitable binding energies of *H and *OH on the Ru overlayer, which lower the activation barrier of the rate-determining Volmer step.The authors acknowledge the support from Hong Kong Research Grant Council (16308420, 16310419, C6011-20G, and HKUST PDFS2021-6S08), Hong Kong Branch of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (SMSEGL20SC01), and Hong Kong Innovation and Technology Commission (ITC-CNERC14EG03).

Determining the structural life of an electric vehicle battery from road loads

Abstract Although the electrical system is important in the development of electric vehicles, the durability of the battery system against mechanical loads and the performance of the battery against shock reactions are just as important. The objective of this study is to develop a methodology to determine the structural life of the battery of the C-platform sports utility vehicle (SUV). For this purpose, a power spectral density (PSD) durability test profile is generated and compared to battery test standards such as ISO 6469:2019, AK-LH 5.21 and SAE J2380. Analytical Virtual Proving Ground (VPG), a multibody dynamics simulation model, is also developed and correlated to test data. The results show that FDS values for AK-LH is higher than the fatigue damage of the collected vehicle data, while the FDS results for ISO standard are lower compared to the vehicle data. The results also indicate that the loads in the longitudinal (x-direction) and lateral (y-direction) directions are different. Therefore, loads of different amplitudes should be used for these directions, contrary to SAE J2380 and USABC standards. Finally, it is concluded that the VPG model can be used for determining the fatigue life when there is no test data, thanks to its high accuracy.

Effect of stacking order on the vibration properties of bilayer black phosphorus

The effect of the stacking order of bilayer black phosphorus (BLBP) on the vibration properties is investigated by using molecular dynamics (MD) simulation and continuum modelling. The results show that the interlayer shear effect plays a very important role in the vibration behaviours of BLBPs. In MD simulation, a negative shear modulus is found in BLBP nanoresonators with stacking orders AA and AA′, which can decrease the natural frequency of the nanoresonators. The prediction of the natural frequency of the BLBP from the orthotropic sandwich plate model (OSPM) agrees with the MD simulation results very well. Moreover, for the vibration of the high-order mode, the interlayer shear modulus of the OSPM along one direction can mainly influence the natural frequency of the vibration mode, with the antinodes strictly aligning the direction for the BLBP. The results are thus important for understanding the dynamic behaviour of multilayer orthotropic nanostructures and designing multilayer orthotropic nanostructure resonators.

Risk Aversion of B2C Cross-Border e-Commerce Supply Chain

In recent years, with the booming development of the B2C cross-border e-commerce industry, the supply chain of B2C cross-border e-commerce faces many potential risk factors, which must be prevented. To solve this problem, this paper studies the supply chain risk factors of B2C cross-border e-commerce and puts forward avoidance strategies. First, the fitness network model of a dual local world is constructed by combining the fitness model with the local world model. Then, the fitness network model of the dual local world is verified by the risk dynamics simulation model to fit the actual network situation. On this basis, the SIRS virus transmission model is constructed to simulate the risk transmission of the B2C cross-border e-commerce supply chain, and the evaluation index system of the supply chain risk immunity ability and external risk intensity are established according to the supply chain risk immunity ability and external risk intensity. AHP is used to calculate the factors that have the greatest influence on supply chain risk immunity and external risk intensity. The results show that: from the point of view of the enterprise’s own risk immunity, it is more necessary to ensure the stability of the company’s capital and to establish a perfect risk monitoring and coping mechanism to avoid risks. From the perspective of enterprise external risk intensity, the risk should be avoided from two aspects of transaction security and logistics.

Femtosecond laser sintering Al nanoparticles: A multiscale investigation of combined molecular dynamics simulation and two-temperature model

The sintering process of Al nanoparticles subject to femtosecond laser irradiation is investigated by using a multiscale approach combining molecular dynamics simulation at atomistic scale and two-temperature model at continuum scale. The temporal evolutions of electron temperature and lattice temperature, atomistic snapshot and structural transformation are calculated to reveal the detailed spatiotemporal information on femtosecond laser sintering Al nanoparticles. Moreover, by studying the temporal evolutions of mean square displacement, radius ratio, shrinkage rate and gyration radius during the sintering process, the impacts of absorbed laser fluence and laser pulse width on the sintering process of Al nanoparticles are probed. The absorbed laser fluence is found to crucially induce whether the Al nanoparticles are to be sintered. Furthermore, the critical absorbed laser fluence to trigger sintering is determined. Whereas, the laser pulse width is found to bring almost no distinctive differences on the process and result of Al nanoparticles sintering.

A systems perspective on early childhood development education in South Africa

South Africa’s basic education system is dysfunctional. It scores last or close to last in a myriad of metrics and delivers learners with some of the worst literacy and numeracy competencies worldwide. A bimodal distribution in the results exists when learners from the richest socioeconomic quintile are performing adequately well, while learners from the poorest quintiles are failing. This paper presents a system dynamics simulation model to describe the causal linkages between improved early childhood and pre-school learning practices on the education system as a whole. The paper investigates the difference in performance between rich and poor communities. Three interventions explore the research question of whether it is the number of enrolments into early childhood development programs that increases a cohort’s school readiness, or rather the quality of the early childhood development programs into which they were enrolled. The results answer the research question for the Western Cape province by showing that increasing the quality of the formal ECD programs leads to a greater percentage of school-ready five year olds than increasing the percentage of enrolled children, but that decreasing community poverty leads to better results than either intervention. The results show the simulation model to be a powerful tool to assist with policy setting and intervention testing for any other province or country by simply changing the input data and calibration.

Influence of Piston Number on Churning Losses in Axial Piston Pumps

Raising the rotational speed of an axial piston pump is useful for improving its power density; however, the churning losses of the piston increase significantly with increasing speed, and this reduces the performance and efficiency of the axial piston pump. Currently, there has been some research on the churning losses of pistons; however, it has rarely been analyzed from the perspective of the piston number. To improve the performance and efficiency of the axial piston pump, a computational fluid dynamics (CFD) simulation model of the churning loss was established, and the effect of piston number on the churning loss was studied in detail. The simulation analysis results revealed that the churning losses initially increased as the number of pistons increased; however, when the number of pistons increased from six to nine, the torque of the churning losses decreased because of the hydrodynamic shadowing effect. In addition, in the analysis of cavitation results, it was determined that the cavitation area of the axial piston pump was mainly concentrated around the piston, and the cavitation became increasingly severe as the speed increased. By comparing the simulation results with and without the cavitation model, it was observed that the cavitation phenomenon is beneficial for the reduction of churning losses. In this study, a piston churning loss test rig that can eliminate other friction losses was established to verify the accuracy of the simulation results. A comparative analysis indicated that the simulation results were consistent with the actual situation. In addition, this study also conducted a simulation study on seven and nine piston pumps with the same displacement. The simulation results revealed that churning losses of the seven pistons were generally greater than those of the nine pistons under the same displacement. In addition, regarding the same piston number and displacement, reducing the pitch circle radius of piston bores is effective in reducing the churning loss. This research analyzes the effect of piston number on the churning loss, which has certain guiding significance for the structural design and model selection of axial piston pumps.

Evaluating Public Health Efforts to Prevent and Control Chronic Disease: A Systems Modeling Approach

The growing burden of chronic disease represents a complex challenge to public health. Innovative approaches, such as system dynamics simulation modeling, can aid public health professionals in understanding such complex issues and identifying effective solutions. This paper describes a system dynamics model and its application in projecting the impacts of evidence-based interventions on chronic disease for the state of Colorado. The development of the model was guided by data and input from subject matter expertise, peer-reviewed literature, and surveillance data. The model includes 28 intervention levers for chronic disease prevention, screening, and management. Interventions were simulated from 2020 to 2050 to project their impact on ten preventable causes of death. The simulations indicated the 6 most impactful interventions by 2050 to be adult smoking prevention, diabetes prevention, smoking cessation, blood pressure management, adult physical activity promotion, and colorectal cancer screening. Together, these 6 interventions could reduce preventable deaths by 7.1%, or 74% of the 9.6% reduction from all 28 interventions combined. This system dynamics model is a flexible tool that could be adapted or extended to include other populations or preventable chronic diseases. Prioritization and wide-scale implementation of the most impactful interventions could significantly reduce preventable deaths resulting from chronic disease.

Reducing opioid use disorder and overdose deaths in the United States: A dynamic modeling analysis.

Opioid overdose deaths remain a major public health crisis. We used a system dynamics simulation model of the U.S. opioid-using population age 12 and older to explore the impacts of 11 strategies on the prevalence of opioid use disorder (OUD) and fatal opioid overdoses from 2022 to 2032. These strategies spanned opioid misuse and OUD prevention, buprenorphine capacity, recovery support, and overdose harm reduction. By 2032, three strategies saved the most lives: (i) reducing the risk of opioid overdose involving fentanyl use, which may be achieved through fentanyl-focused harm reduction services; (ii) increasing naloxone distribution to people who use opioids; and (iii) recovery support for people in remission, which reduced deaths by reducing OUD. Increasing buprenorphine providers’ capacity to treat more people decreased fatal overdose, but only in the short term. Our analysis provides insight into the kinds of multifaceted approaches needed to save lives.

Optimization Design for Suspension System Based on Response Surface Method and NCGA Algorithm

For effective and quick selection of hard point coordinate parameters of suspension to improve the handling stability of vehicles, an optimization method was put forward to some certain suspension system by combining the response surface method and NCGA algorithm. A dynamics simulation model was established first to the Macpherson suspension system of some certain mini-van and the sensitivity analysis was carried out to hard point coordinates of the corresponding suspension to find the coordinate parameters whose sensitivities are higher; moreover, an approximate mathematical model was established between the wheel alignment parameters and the selected coordinate parameters in accordance with the response surface method and the corresponding accuracy verification was carried out; and the positioning parameters were grouped rationally and the unified objective function was established by utilizing the direct weighting method; in addition, optimization design was carried out to the established objective function by combining the neighborhood cultivation genetic algorithm (NCGA). Results indicate that the optimized positioning parameter variables are reduced in different degrees so as to further improve the handling stability of vehicles and verify some certain effectiveness of our methods.

Erratum: Symplectic particle-in-cell model for space-charge beam dynamics simulation [Phys. Rev. Accel. Beams 21 , 054201 (2018)

Erratum: Symplectic particle-in-cell model for space-charge beam dynamics simulation [Phys. Rev. Accel. Beams <b>21</b> , 054201 (2018)

Aphrodisiac Performance of Bioactive Compounds from Mimosa pudica Linn.: In Silico Molecular Docking and Dynamics Simulation Approach.

Plants and their derived molecules have been traditionally used to manage numerous pathological complications, including male erectile dysfunction (ED). Mimosa pudica Linn. commonly referred to as the touch-me-not plant, and its extract are important sources of new lead molecules in drug discovery research. The main goal of this study was to predict highly effective molecules from M. pudica Linn. for reaching and maintaining penile erection before and during sexual intercourse through in silico molecular docking and dynamics simulation tools. A total of 28 bioactive molecules were identified from this target plant through public repositories, and their chemical structures were drawn using Chemsketch software. Graph theoretical network principles were applied to identify the ideal target (phosphodiesterase type 5) and rebuild the network to visualize the responsible signaling genes, proteins, and enzymes. The 28 identified bioactive molecules were docked against the phosphodiesterase type 5 (PDE5) enzyme and compared with the standard PDE5 inhibitor (sildenafil). Pharmacokinetics (ADME), toxicity, and several physicochemical properties of bioactive molecules were assessed to confirm their drug-likeness property. Molecular dynamics (MD) simulation modeling was performed to investigate the stability of PDE5–ligand complexes. Four bioactive molecules (Bufadienolide (−12.30 kcal mol−1), Stigmasterol (−11.40 kcal mol−1), Isovitexin (−11.20 kcal mol−1), and Apigetrin (−11.20 kcal mol−1)) showed the top binding affinities with the PDE5 enzyme, much more powerful than the standard PDE5 inhibitor (−9.80 kcal mol−1). The four top binding bioactive molecules were further validated for a stable binding affinity with the PDE5 enzyme and conformation during the MD simulation period as compared to the apoprotein and standard PDE5 inhibitor complexes. Further, the four top binding bioactive molecules demonstrated significant drug-likeness characteristics with lower toxicity profiles. According to the findings, the four top binding molecules may be used as potent and safe PDE5 inhibitors and could potentially be used in the treatment of ED.

Reliability-Based Multivehicle Path Planning Under Uncertainty Using a Bio-Inspired Approach

Abstract Identifying a reliable path in uncertain environments is essential for designing reliable off-road autonomous ground vehicles (AGVs) considering postdesign operations. This article presents a novel bio-inspired approach for model-based multivehicle mission planning under uncertainty for off-road AGVs subjected to mobility reliability constraints in dynamic environments. A physics-based vehicle dynamics simulation model is first employed to predict vehicle mobility (i.e., maximum attainable speed) for any given terrain and soil conditions. Based on physics-based simulations, the vehicle state mobility reliability in operation is then analyzed using an adaptive surrogate modeling method to overcome the computational challenges in mobility reliability analysis by adaptively constructing a surrogate. Subsequently, a bio-inspired approach called Physarum-based algorithm is used in conjunction with a navigation mesh to identify an optimal path satisfying a specific mobility reliability requirement. The developed Physarum-based framework is applied to reliability-based path planning for both a single-vehicle and multiple-vehicle scenarios. A case study is used to demonstrate the efficacy of the proposed methods and algorithms. The results show that the proposed framework can effectively identify optimal paths for both scenarios of single and multiple vehicles. The required computational time is less than the widely used Dijkstra-based method.

SIMULATION OF THE LEVEL OF PREPAREDNESS IN A FUTURE NATURAL DISASTER. CASE STUDY FILOMENA

ABSTRACT: Disaster risk is a social process characterized by the coincidence, at the same time and place, of potentially dangerous physical phenomena and socioeconomic elements exposed to these phenomena in a condition of vulnerability. Therefore, forces derived from society and nature are at work in determining the existence of risk and its levels. Neither of these two elements are stable or permanent over time. They undergo continuous changes and variations. In this sense, this work presents a system dynamics simulation model of the degree of preparedness in the disaster risk management process at the level of an autonomous community. All this with the aim of raising awareness of the problematic of the social and economic impact of this type of physical phenomena. This model is applied to the context of the Filomena storm (natural disaster that took place in Spain on January 7, 2021) in order to validate its usefulness in a real case study. The model is implemented in two simulations and results are compared. In the first simulation, actual data associated with the policies, reports and descriptions of the community of Madrid during the 120 days prior to the event are introduced according to certain variables within the Sendai risk reduction framework (forecast errors, available information, CO2 emissions, recycling and commodity index prices). With that, the value " of the "Degree of Preparedness" achieved by the capital before the storm is obtained. In the second simulation, these input variables of the model are modified to analyze the effect it would have had on the "Degree of Preparedness". Key Words: Simulation, Vensim, Risk Management, Storm Filomena, Natural Disasters.

Numerical Prediction of Unsteady Aerodynamics of a Ducted Fan Unmanned Aerial Vehicle in Hovering

Recently, ducted fan unmanned aerial vehicles (UAVs) have attracted considerable attention due to their potential for application in both civil and military missions. Compared with free propellers, the presence of duct can in principle decrease the flow contraction after propeller, and gives the potential to fly efficiently with high security, compact structure, and low noise. In the present study, a ducted fan UAV is designed using the open source code OpenProp. The computational fluid dynamics (CFD) simulation model using sliding mesh technique is established and validated as a reliable tool for highly vortical flows by propeller thrust experiment. The effect of the duct, revolution speed, and distance between propellers on the aerodynamic characteristics of the ducted fan UAV is evaluated in detail. Results show that the unducted coaxial upper and lower propellers generate 3.8%, 4.3% more thrust than the unducted single propellers, respectively, and the unducted upper and lower propellers generate 55.9%, 34.9% more thrust than ducted propellers, respectively. The ducted fan UAV generates 5.7% more thrust and consumes 39.1% less power than the unducted coaxial propellers. The thrust of the ducted fan UAV increases first and then follows with a decreased tendency as the distance between propellers increases.

Simulation Research of the n-Butanol Proportion Influence on HCCI Combustion of Free-Piston Diesel Engine Generators

For researching the influence of n-butanol proportion in diesel fuel on homogeneous charge compression ignition (HCCI) combustion of the free-piston diesel engine generator (FPDEG), a three-dimensional (3D) moving mesh computational fluid dynamics (CFD) simulation model of a FPDEG prototype was developed. A detailed chemical reaction mechanism of diesel fuel was selected as the HCCI combustion mechanism and coupled in the established HCCI combustion simulation model of the FPDEG prototype. The validity of the established HCCI combustion simulation model is proved by comparing the simulation and experimental pressure curves under the condition of pure diesel fuel. The simulation results of different n-butanol proportions in diesel fuel showed that as the n-butanol proportion increased from 0 to 60%, the maximum heat release rate decreased to 59.6 J/deg, the calculated indicated thermal efficiency augmented to 4.6%, the calculated indicated mean effective pressure increased to 0.057 MPa, and the final NOx and CO content decreased to 0.239 and 0.57 g/kg fuel, respectively, but the final soot content increased to 0.000562 g/kg fuel. Therefore, the n-butanol proportion of diesel fuel played a vital role in combustion and emission progress of the FPDEG.

En route for molecular dynamics simulation of a living cell

Creating an in silico all-atom whole-cell model for molecular dynamics (MD) simulation is one of the best ways to quantitatively understand the basic structure and function of cells in terms of the laws of physics and chemistry. The heavy use of graphics processing units (GPUs), the exponential growth of supercomputing power, and the emergence of MD simulation-specific supercomputers lay the groundwork for the MD simulation of molecular machinery. Moreover, the involvement of artificial intelligence (AI) will not only improve the accuracy of the simulation but also significantly accelerate the sampling efficiency. However, several underlying critical puzzles prevent in silico all-atom whole-cell modeling, which is the holy grail of MD simulation. From this perspective, we briefly reviewed the accomplishments of present techniques and hardware as well as provided insight to address the challenge of MD simulation of a living cell. With the rapid advancements in computational hardware, AI, and experimental cell biology, it would be possible to achieve this overarching goal.

Effects of tool geometry on tungsten removal behavior during nano-cutting

Although the researches in effects of tool geometry on the removal behavior of many metals have been studied, the deformation and removal mechanisms of tungsten have changed greatly due to the higher brittleness of tungsten compared with other metals and the research on the removal behavior of tungsten involved changing of tool geometry during nano-cutting has not been reported, which limits the development of high precision manufacturing of tungsten components. Herein, molecular dynamics (MD) simulation model of nano-cutting tungsten was established, and the material removal behavior induced by changing of tool geometry was comprehensively studied. The results showed that a larger positive rake angle or larger clearance angle or smaller edge radius of the tool was beneficial to reduce the surface roughness, elastic recovery, thickness of subsurface damage layer, cutting force, cutting temperature, friction coefficient, and maximum stress while the surface presented less residual compressive stress or even tensile stress. In the plastic deformation dominated by phase transition and dislocation slip, the region of 1/2<111> dislocation line presented compressive stress state whereas the region of <100> dislocation line presented tensile stress state during nano-cutting tungsten. Meanwhile, there was no phase transition from BCC structure to other crystal structures, but rather from ordered structure to disordered structure (amorphous structure). The correlation between amorphous phase transition and dislocation slip was affected by the tool geometry owing to the fact that the temperature and stress were different under different tool geometries. The research findings provide a comprehensive theoretical basis for the micro removal behavior of tungsten and technical reference for the design of tools in nano-cutting.

Exploring ways to respond to rising obesity and diabetes in the Caribbean using a system dynamics model.

Diabetes and obesity present a high and increasing burden of disease in the Caribbean that have failed to respond to prevention policies and interventions. These conditions are the result of a complex system of drivers and determinants that can make it difficult to predict the impact of interventions. In partnership with stakeholders, we developed a system dynamics simulation model to map the system driving diabetes and obesity prevalence in the Caribbean using Jamaica as a test case. The study aims to use the model to assess the magnitude changes necessary in physical activity and dietary intake to achieve global targets set by the WHO Global Action plan and to test scenarios for interventions to reduce the burden of diabetes and obesity. Continuing current trends in diet, physical activity, and demographics, the model predicts diabetes in Jamaican adults (20+ years) to rise from 12% in 2018 to 15.4% in 2030 and 20.9% by 2050. For obesity, it predicts prevalence to rise from 28.6% in 2018 to 32.1% by 2030 and 39.2% by 2050. The magnitude change necessary to achieve the global targets set by the World Health Organization is so great as to be unachievable. However, a combination of measures both upstream (including reducing the consumption of sugar sweetened beverages and ultra processed foods, increasing fruit and vegetable intake, and increasing moderate-to-vigorous activity) at the population level, and downstream (targeting people at high risk and with diabetes) can significantly reduce the future burden of diabetes and obesity in the region. No single intervention reduces the prevalence of these conditions as much as a combination of interventions. Thus, the findings of this model strongly support adopting a sustained and coordinated approach across various sectors to synergistically maximise the benefits of interventions.

Determinants of performance drivers in online food delivery platforms: a dynamic performance management perspective

PurposeThis study aims to demonstrate that the Dynamic Performance Management (DPM) framework, integrating performance management with system dynamics modelling, enables decision-makers to identify sustainable strategies in online food delivery platforms, thereby avoiding company failure.Design/methodology/approachThis study undertakes a multistep methodological approach. After the literature review, a retrospective case study approach was used. To build the DPM framework and the system dynamics simulation model, primary and secondary data were collected and analysed.FindingsThis study by adopting the DPM perspective highlights the critical role performance drivers play to assess the viability of alternative growth strategies in food delivery digital platforms. As such, the findings complement extant studies which highlighted the need for adopting a dynamic perspective in Performance Measurement and Management (PMM), particularly in complex and turbulent environments. Findings also highlight that in food delivery platforms, network effects may result insufficient to reach a critical volume of users and factors such as key drivers impacting platform attractiveness must be considered to design effective PMM.Research limitations/implicationsFuture studies may apply the DPM framework here suggested to multiple digital platforms, to validate this study's findings.Practical implicationsThis paper offers a guidance to practitioners and scholars to design effective PMM in food delivery digital platforms.Originality/valueThis study offers an innovative perspective to analyse the interdependences among main mechanisms underpinning the performance of food delivery platforms. As such, it contributes to enrich prior PMM literature and addresses the call for more empirical and theoretical PMM contributions in fast-changing and turbulent environments.